Compounds with intense light absorption in 550 to 620 nm, particularly compounds having a wavelength of absorption maximum (λmax) in 550 to 620 nm, are used as optical recording materials for forming optical recording layers of optical recording media such as DVD-R.
As the above optical recording materials, there are many reports with cyanine compounds having an indole ring since they have merits of high sensitivity and compatibility with high-speed recording. For example, Patent Documents 1 and 2 report low temperature-decomposable cyanine compounds in which a metallocene-containing group is introduced into a side chain on the nitrogen atom, whereas Patent Document 3 reports low temperature-decomposable cyanine compounds in which a benzyl group is introduced into the position-3. Patent Document 1 also describes use of perchlorate as an anion component of cyanine compounds can further decrease the decomposition temperature.
If the optical recording material used in the optical recording layer of optical recording medium releases large heat on its decomposition, recording properties will be deteriorated due to thermal interference of recording pits. Optical recording materials are, therefore, desired to decompose not only at lower temperature but also less exothermically. For example, cyanine compounds containing perchlorate anion, which is effective for lowering the decomposition temperature, release large heat on decomposition, possibly deteriorating jitter properties of optical recording media.                Patent Document 1: Japanese Patent Laid-open Publication No. 2003-171571        Patent Document 2: Japanese Patent Laid-open Publication No. 2004-195765        Patent Document 3: Japanese Patent Laid-open Publication No. 2003-231359        